Optimal Infusion Rate of Norepinephrine for Prevention of Spinal Hypotension for Cesarean Delivery: A Randomized Controlled Trial, Using Up-Down Sequential Allocation

Norepinephrine has recently been suggested to be as effective as phenylephrine for the prevention of hypotension after spinal anesthesia for cesarean delivery. Moreover, compared to phenylephrine, norepinephrine may be superior in maintaining heart rate (HR) and consequently, cardiac output (CO). A recent study demonstrated that norepinephrine given as a single intravenous bolus is approximately 13 times more potent than phenylephrine. However, it is uncertain whether this finding can be applied when these vasopressors are administered as infusions. Therefore, the optimum infusion rate of norepinephrine remains unknown. We aimed to determine the median effective dose (ED50; defined as the rate of vasopressor infusion required to prevent spinal hypotension in 50% of subjects) of both drugs needed to maintain maternal systolic blood pressure within 20% of the baseline after spinal anesthesia for cesarean delivery and to derive the relative potency ratio.